THE HEART
© 2016 Paul Billiet ODWS
The heart - function
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The heart is a hollow muscle
It collects blood returning in veins
It pumps blood into arteries
Direction of blood controlled by valves
Veins drain into….
atria which pump blood through…
atrio-ventricular (bicuspid & tricuspid) valves
direct blood into …
ventricles which pump blood through …
arterial/semi-lunar valves direct blood into…
arteries carry blood away to the tissues.
© 2016 Paul Billiet ODWS
THE MAJOR FACTORS
CONTROLLING HEART
BEAT
• The heart muscle tissue shows an inherent
contraction without connection to nerves
• The heart beat is initiated and controlled at
the SINO-ATRIAL NODE (the pacemaker).
© 2016 Paul Billiet ODWS
Stimulates
Inhibits
Higher
centres
High CO2
Medulla
Cardioinhibitory centre
&
Cardioacceleratory centre
Vagus nerve
Slows heart
Accelerans nerve
Speeds up heart
Spinal
cord
Adrenal gland
© 2016 Paul Billiet ODWS
Epinephrin
Sino-atrial
node
“Pacemaker”
Heart
Control of heart beat frequency
- Nervous control
• Nerve stimuli from the VAGUS NERVE will
slow the heart beat
• Stimuli from the ACCELERANS NERVE will
speed up the heart beat.
© 2016 Paul Billiet ODWS
Control of heart beat frequency
- Hormonal control
• EPINEPHRIN (aka ADRENALIN) speeds up
the heart beat (direct effect)
• NOREPINEPHRIN (aka NORADRENALIN)
indirectly causes a slowing of the heart beat.
© 2016 Paul Billiet ODWS
THE CARDIAC CYCLE
• Diastole
= muscles relaxed
= low pressure in the heart
• Systole
= muscles contracted
= high pressure in the heart
• Sound: LUB DUB pause
© 2016 Paul Billiet ODWS
DIASTOLE
• Atria and ventricle walls relax, pressure
drops in the ventricles
• Semi-lunar valves shut = DUB, catching the
backflow from the arteries
(pressure in the ventricles < pressure in the
arteries)
• Atria fill with blood returning from the veins
• Blood drains into the ventricles
© 2016 Paul Billiet ODWS
SYSTOLE
• Atria muscles contract forcing blood into the
ventricles
• Papillary muscles contract tensing the tendons to
the atrio-ventricular valves (bicuspid and tricuspid)
• Ventricle muscles contract. Pressure increases
• Atrio-ventricular valves shut = LUB and hold the
blood in the ventricles.
Pressure in the ventricles rises
• Semi-lunar valves open
(pressure in ventricles > pressure in arteries)
• Blood flows away from the heart
© 2016 Paul Billiet ODWS
Back to DIASTOLE
• Atria and ventricles relax
(pressure in ventricles < pressure in the
arteries)
• Semilunar valves shut = DUB
© 2016 Paul Billiet ODWS
Wiggers pressure diagram
The coronary circulation
Colin Berry et al European Heart Journal (2007)
28, 278–291 doi:10.1093/eurheartj/ehl446
Occlusions of the coronary
arteries
Abreu G, Nabais S, Enes V, Marques J, Costa J, Correia A. Arcada coronária --- uma anomalia rara da circulac¸ão
coronária 2014;33:241.e1---241.e5.
Causes and consequences
• Causes
Atherosclerosis = Build up of cholesterol rich
plaques – age, diet, hereditary
Blood clot formation (thrombosis)
Nicotine (vasoconstriction)
• Consequences
Ischemia - poor blood flow to heart tissues
Angina - chest pains
Myocardial infarction - heart attack.
© 2016 Paul Billiet ODWS